[boost] Graph_traits and Graph

From: Jannel Rémi (remj_at_[hidden])
Date: 2005-02-02 04:20:29

        Hello All,

    I started to use boost a few weeks ago and i still have got some problems with the graph_traits theory. In fact, it seems that you use a graph_traits to stock the type of the data used for the Graph (given as a template) such as vertex_descriptor or in_edge iterator. 

To keep this you use something like:

 typedef typename Graph::vertex_descriptor      vertex_descriptor;

which means that you get this type from Graph::vertex_descriptor.

Now, if i want to wite an algorithm which will search for all the vertices for example, i'll have to use my Graph as a template and i'll get the vertex type for example using 
typedef typename graph_traits<Graph>::vertex_descriptor vertex_descriptor;

That's why I wanted to ask you why this method is used instead of just

typedef typename Graph::vertex_descriptor vertex_descriptor;

used in the class graph_traits definition.

I hope i made me understandable!

Thanks a lot

Koopajah